Versatile 3-d picture format

ABSTRACT

A 3-D picture is provided as follows. A pair of pictures (LP, RP) is provided that comprises a first picture (LP) being intended for one eye of a viewer, and a second picture (RP) being intended for the other eye of the viewer. In addition, a depth map (DM) specifically dedicated to the first picture (LP) is provided. The depth map (DM) comprises depth indication values. A depth indication value relates to a particular portion of the first picture (LP) and indicates a distance between an object at least partially represented by that portion of the first picture and the viewer. Such a 3-D picture allows a satisfactory 3-D visual rendering on a great variety of display devices. Preferably, the 3-D picture is supplemented with rendering guidance data (GD) that specifies respective parameters for respective rendering contexts. These respective parameters preferably relate to generating a shifted viewpoint picture from the first picture (LP) and the depth map (DM).

FIELD OF THE INVENTION

An aspect of the invention relates to a method of providing a 3-Dpicture that comprises a pair of images, one picture being intended forone eye of the viewer, the other picture being intended for the othereye of the viewer. The 3-D picture may form part of, for example, asequence of 3-D pictures that have a similar format so as to constitutea video. Other aspects of the invention relate to a 3-D pictureprovision system, a signal that conveys a 3-D picture, a method ofrendering a 3-D picture, a 3-D picture rendering system, and a computerprogram product for a programmable processor.

BACKGROUND OF THE INVENTION

A visual 3-D rendering may be obtained on the basis of a signal thatcomprises a pair of pictures: a left picture and a right pictureintended for the left eye and the right eye, respectively, of a viewer.In the case of a video, the signal will comprise a sequence of suchpicture pairs. The left and right pictures comprised therein maydirectly be rendered on a stereoscopic display device, which may requirea viewer to wear a pair of glasses. A left-eye glass passes a renderedleft picture to the left eye. A right-eye glass passes a rendered rightpicture to the right eye. For example, the display device mayalternately display rendered left pictures and rendered right pictures.In that case, the left-eye glass is made transparent when a renderedleft picture is displayed, and is opaque otherwise. Similarly, theright-eye glass is made transparent when a rendered right picture isdisplayed, and is opaque otherwise.

A signal that comprises a pair of pictures, or a sequence of picturepairs that constitutes a 3-D video, as described in the precedingparagraph, is typically generated for a particular rendering context interms of, for example, screen size and viewing distance. The particularrendering context may be, for example, a cinema with a screen that is 12meters wide and where viewers are typically sitting at a distance of 18meters from the screen. In case a rendering context is different fromthe rendering context for which the signal has been generated, the 3-Dvideo will look different. For example, in case the 3-D video that hasbeen generated for the cinema is rendered on a home video set, a viewerwill experience a different visual impression that in the cinema. Deptheffects will typically be smaller and, moreover, there may be anapparent depth shift in the sense that an object which appears to be farbehind the screen in the cinema appears to be nearly in front of thescreen of the home video set.

A viewer, who watches a 3-D video in a private environment, such as athome, may wish to adjust depth effects so as to obtain a rendering thatthe user experiences as most pleasant. In principle, it is possible toachieve this by means of an interpolation, or an extrapolation, which isbased on each pair of images comprised in the 3-D video. In effect, aleft picture and a right picture are compared so as to obtain aso-called disparity map expressing differences between these pictures,in particular in terms of horizontal displacement. Depth effectsadjustments may be expressed in the form of a modified disparity map,which is used to generate a new pair of images. Such a process ofinterpolation, or extrapolation, is relatively complex and, therefore,relatively costly. Moreover, such a process may introduce perceptibleartifacts, which may be less pleasant to the viewer.

United States patent application published under number 2005/0190180describes a method for customizing scene content, according to a user ora cluster of users, for a given stereoscopic display. Customizationinformation about the user is obtained. A scene disparity map for a pairof given stereo images is also obtained. An aim disparity range for theuser is determined A customized disparity map is generated thatcorrelates with the user's fusing capability of the given stereoscopicdisplay. The stereo images are rendered or re-rendered for subsequentdisplay.

SUMMARY OF THE INVENTION

There is a need for a versatile 3-D video signal that allowssatisfactory rendering on a great variety of display devices. Theindependent claims, which are appended to the description, definevarious aspects of the invention that better address this need. Thedependent claims define additional features for implementing theinvention to advantage.

In accordance with an aspect of the invention, a 3-D picture is providedas follows. A pair of pictures is provided that comprises a firstpicture being intended for one eye of a viewer, and a second picturebeing intended for the other eye of the viewer. In addition, a depth mapspecifically dedicated to the first picture is provided. The depth mapcomprises depth indication values. A depth indication value relates to aparticular portion of the first picture and indicates a distance betweenan object at least partially represented by that portion of the firstpicture and the viewer.

The pair of pictures typically represents a scene from differentviewpoints. At a rendering end, a shifted viewpoint picture may begenerated from the first picture and the depth map. The shiftedviewpoint picture represents the scene from a viewpoint that isdifferent from that of the first picture. The shifted viewpoint pictureand the second picture jointly constitute a new picture pair, whichallows a visual 3-D rendering different from that obtained by displayingthe first picture and the second picture as such. An appropriaterendering can be obtained by adjusting the amount of shift, in terms ofviewpoint, of the shifted viewpoint picture with respect to the firstpicture. The amount of shift will typically be rendering contextdependent: a larger screen or a smaller screen can be accommodated forby an appropriate amount of shift. Importantly, the shifted viewpointpicture can be generated in a relatively precise yet simple fashion fromthe first picture and the depth map, which is specifically dedicated tothe first picture. Accordingly, a satisfactory visual 3-D rendering canbe obtained on a great variety of display devices in a cost-efficientmanner.

It should be noted that a 3-D picture, or a sequence thereof, which hasbeen provided in accordance with the invention, is also particularlysuited for rendering by means of auto-stereoscopic display devices. Sucha rendering typically involves generating multiple shifted viewpointpictures, each of which represents a scene concerned from a particularviewpoint. These multiple shifted viewpoint pictures can be generated ina relatively simple fashion from the first picture and the depth map,which is specifically dedicated to the first picture. The second picturemay effectively be ignored for the purpose of auto-stereoscopicrendering. Accordingly, the depth map may effectively be used for twopurposes: firstly for the purpose of adapting to a particular renderingcontext and, secondly, for the purpose of generating multiple shiftedviewpoint pictures in case of rendering by means of an auto-stereoscopicdisplay device.

It should further be noted that a 3-D picture, or a sequence thereof,which has been provided in accordance with the invention, will typicallycomprise a modest amount of additional data compared with a basic 3-Dpicture that comprises a pair of pictures only. This is because a depthmap will typically comprise a modest amount of data compared with apicture, which constitutes a visual representation of a scene. A depthmap may have a lower resolution than a picture to which the depth mappertains. Furthermore, a depth map needs only to comprise a single valuefor a pixel or a cluster of pixels, whereas a picture typicallycomprises various values for a pixel: a luminance value, and twochrominance values. Accordingly, a storage medium, such as, for example,a DVD disk, which provides sufficient capacity for storing a basic 3-Dvideo, will typically also provides sufficient capacity for storing a3-D video that has been provided in accordance with the invention.Similarly, a transmission channel that allows transmission of a basic3-D video, will typically also allow transmission of a 3-D video thathas been provided in accordance with the invention. The aforementionedadvantages can thus be achieved with only a relatively small investmentin terms of storage capacity, or bandwidth, or both.

An implementation of the invention advantageously comprises one or moreof the following additional features, which are described in separateparagraphs that correspond with individual dependent claims.

Preferably, the rendering guidance data specifies respective parametersfor respective rendering contexts. The respective parameters relate togenerating a shifted viewpoint picture from the first picture and thedepth map, which is specifically dedicated to the first picture.

The rendering guidance data preferably comprises a set of parameters fora first stereo mode, and a set of parameters for a second stereo mode.In the first stereo mode, a shifted viewpoint picture, which isgenerated from the first picture and the depth map, constitutes arendered first picture, and the second picture constitutes a renderedsecond picture. In the second stereo mode, the first picture constitutesa rendered first picture, and a shifted viewpoint picture, which isgenerated from the first picture and the depth map, constitutes arendered second picture.

The aforementioned respective sets of parameters are preferably providedwith a definition of a first stereo strength range in which the firststereo mode should apply, and a second stereo strength range in whichthe second stereo mode should apply.

The rendering guidance data may define respective maximum parallax shiftvalues for respective depth indication values.

The rendering guidance data may define respective parallax offset valuesfor respective screen sizes.

The rendering guidance data may comprise an indication of depth mapprecision.

A background picture that is specifically dedicated to the first pictureis preferably provided.

In addition, an alpha-map that is specifically dedicated to the firstpicture is preferably provided. The alpha-map defines gradualtransitions in a shifted viewpoint picture that can be generated fromthe left picture, the depth map and the background picture.

The present invention is further embodied in a method as claimed inclaim 1 wherein the first, the second picture and the depth map areprovided at a resolution tuned to a predetermined bandwidth for transferof the signal and wherein extra frames are encoded providing furtherdata for use in rendering based on an image and depth components.

The underlying idea is that the first, the second picture and the depthmap may be provided at a resolution tuned to the available bandwidth fortransfer of the first and second picture in the original resolution. Theextra frames in turn are provided in order to provide further data foruse in rendering based on an image and depth components.

The present invention is further embodied in a 3-D picture provisionsystem according to the first, the second picture and the depth map areprovided at a resolution tuned to a pre-determined bandwidth fortransfer of the signal and wherein extra frames are encoded providingfurther data for use in rendering based on an image and depthcomponents.

The present invention is further embodied in a signal that conveys a 3-Dpicture, comprising: a pair of pictures comprising a first picture (LP)being intended for one eye of a viewer, and a second picture (RP) beingintended for the other eye of the viewer; a depth map (DM) specificallydedicated to the first picture (LP), the depth map comprising depthindication values, a depth indication value relating to a particularportion of the first picture and indicating a distance between an objectat least partially represented by that portion of the first picture andthe viewer, and wherein the first, the second picture and the depth mapare provided at a resolution tuned to a predetermined bandwidth fortransfer of the signal and wherein extra frames are encoded providingfurther data for use in rendering based on an image and depthcomponents.

The present invention is further embodied in a storage medium comprisinga signal according to claim 19.

A detailed description, with reference to drawings, illustrates theinvention summarized hereinbefore as well as the additional features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates a 3-D video generationsystem.

FIG. 2 is a conceptual diagram that illustrates a versatile 3-D videosignal, which the 3-D video generation system provides.

FIG. 3 is a conceptual diagram that illustrates a first stereo mode,which is possible with the versatile 3-D video signal.

FIG. 4 is a conceptual diagram that illustrates a second stereo mode,which is possible with the versatile 3-D video signal.

FIG. 5 is a conceptual diagram that illustrates a supplemented versatile3-D video signal.

FIG. 6 is a data diagram that illustrates an example of renderingguidance data that may be comprised in the supplemented versatile 3-Dvideo signal.

FIG. 7 is a data diagram that illustrates another example of renderingguidance data that may be comprised in the supplemented versatile 3-Dvideo signal.

FIG. 8 is a data diagram that illustrates yet another example ofrendering guidance data that may be comprised in the supplementedversatile 3-D video signal.

FIG. 9 is a block diagram that illustrates a 3-D video supplementationsystem, which is capable of providing the supplemented versatile 3-Dvideo signal.

FIG. 10 is a flow chart diagram that illustrates a series of steps thatthe 3-D video signal supplementation system may carry out.

FIG. 11 is a block diagram that illustrates a video rendering system,which allows a stereoscopic rendering based on the versatile 3-D videosignal.

FIG. 12 is a block diagram that illustrates an alternative videorendering system, which comprises an auto-stereoscopic display device.

FIG. 13, shows an overview for BD players for monoscopic video, 30 Hzprogressive or 60 Hz interlaced and.

FIG. 14, shows an example on how an L′R′D′ signal can be efficientlycoded using AVC/H264 or MVC having approximately the same bit-rate asrequired for a monoscopic 1080p 24 Hz mono signal.

FIG. 15, shows various modes and options for new 3D Blu-rayapplications.

FIG. 16, shows an example of a bit-rate and memory efficient jointcoding (with AVC/H264) of L R D (2:2:1 frame rate ratio).

FIG. 17, shows a coding example wherein depth and transparencycomponents are encoded at 12 Hz and wherein depth and transparencyrelate to different phases.

FIG. 18, shows a coding example having mixed 12 and 24 Hz depthcomponents.

FIG. 19, shows frame interleaving and compression in LRDD′ mode, andshows the respective contents of the D and D′ frames.

FIG. 20, shows various subsampling methods in order to create room fordepth and transparency.

DETAILED DESCRIPTION

FIG. 1 illustrates a 3-D video generation system GSY. The 3-D videogeneration system GSY comprises a pair of cameras, a right camera RCAMand a left camera LCAM, a recording processor RPR, and a storage mediumSTM. A depth scanner DS is associated with the left camera LCAM. Thepair of cameras RCAM, LCAM is directed towards a scene SCN as to capturea 3-D video of the scene SCN. The scene SCN comprises various objects,such as, for example, a person, a tree, a house, and the sun in the sky.Each object has a given distance with respect to the pair of cameras,which may be regarded as a virtual observer watching the scene SCN.

The right camera RCAM and the left camera LCAM may each be aconventional camera. The recording processor RPR may comprise, forexample, an instruction-executing device and a program memory into whicha set of instructions has been loaded that define operations of therecording processor RPR, which will be described hereinafter. Thestorage medium STM may be in the form of, for example, a hard disk, awritable optical disk, or a solid-state memory. The depth scanner DS maycomprise, for example, a laser beam that can be steered in variousdirections, and a sensor that detects reflections of the laser beam. Asanother example, the depth scanner DS may comprise a radar imagingmodule. As yet another example, the depth scanner may even be in theform of a human being who creates depth maps off-line.

The 3-D video generation system GSY basically operates as follows. Thepair of cameras RCAM, LCAM provides a basic 3-D video of the scene SCN,which is formed by a sequence of picture pairs. A picture pair comprisesa right picture and a left picture. The right picture, which is capturedby the right camera RCAM, is intended for the right eye of a humanobserver. The left picture, which is captured by the left camera LCAM,is intended for the left eye of a human observer.

The right camera RCAM and the left camera LCAM have a particularpositional relationship with respect to each other. This positionalrelationship may be defined by a typical rendering context in terms of,for example, screen size and a viewing distance. For example, the basic3-D video, which comprises a sequence of right pictures and a sequenceof left pictures that are interrelated, may be intended for display in acinema with a typical screen size of 12 meters and a typical viewingdistance of 18 meters.

The depth scanner DS carries out a series of depth measurements for aleft picture, while the left camera LCAM captures the left picture. Adepth measurement provides a depth indication value for a particularportion of the left picture concerned. Such a particular portion maycomprise a single pixel or a cluster of pixels, which may constitute ablock. For example, the left picture may effectively be divided intovarious blocks of pixels, whereby the depth scanner DS providesrespective depth indication values for respective blocks of pixels. Fora block of pixels that partially represents the person in the scene SCN,the depth scanner DS may provide a depth indication value thatrepresents the distance between the person in the scene SCN and virtualobserver.

The recording processor RPR may thus generate a depth map for a leftpicture that comprises the respective depth indication values that thedepth scanner DS provides for this left picture. Such a depth map may beregarded as an extension of the left picture, which adds an extradimension from 2-D to 3-D. In other words, the depth map adds a depthindication value to a pixel of the left picture, which comprises aluminance value, and a pair of chrominance values for the pixelconcerned. The depth map is specifically dedicated to the left picture:a depth indication value is associated with at least one pixel in theleft picture, whereas it may not be possible to associate the depthindication value with any pixel in the right picture. The depth map mayhave a lower resolution than the left picture. In that case, neighboringpixels share the same depth indication value, which applies to a clusterof pixels.

It should be noted that depth indication values may be provided innumerous different forms. For example, a depth indication value may bein the form of a parallax value, which is defined with respect to atypical screen width, a typical viewing distance, and a typical eyedistance. Such a parallax value can be converted into a distance value.

The recording processor RPR may further generate a background picturefor the left picture. The background picture represents objects, orportions thereof, that are occluded in the left picture by otherobjects, which have a foreground position. That is, the backgroundpicture provides information about what is behind an object in the leftpicture that has a foreground position. This information can be used toadvantage in generating a 3-D representation of the left image on thebasis of the depth map. Referring to FIG. 1, the house has a backgroundposition, whereas the person has a foreground position and may thereforeocclude a portion of the house in a left picture. The background picturemay thus comprise, at least partially, the portion of the house that isoccluded by the person in the left picture. It should be noted that thebackground picture may further comprise a depth map specificallydedicated thereto. Stated otherwise, the background picture may comprisetexture information as well as depth information, which provides a 3-Drepresentation of occluded objects. The recording processor RPR maygenerate the background picture for the left picture on the basis of,for example, information comprised in the right picture.

The recording processor RPR may further generate an alpha-map, which isspecifically dedicated to a left picture. An alpha-map canadvantageously be used for providing gradual transitions in a shiftedviewpoint picture that is generated from the left picture, the depth mapand the background picture. This contributes to perceived image quality.The alpha-map may be regarded as a set of gross weighting coefficients,which may determine a degree of contribution from the left picture and adegree of contribution from the background picture for a particularportion of the shifted viewpoint picture. Such an alpha-map can definedifferent blending parameters for different picture portions, whichallows smooth transitions.

The recording processor RPR generates a versatile 3-D video signal VS byadding elements to the basic 3-D video, which the right camera RCAM andthe left camera LCAM provide. These elements include depth maps and,optionally, background pictures and alpha-maps, which may be generatedas described hereinbefore. The storage medium STM stores the versatile3-D video signal VS. The versatile 3-D video signal VS may be subject tofurther processing, which contributes to satisfactory 3-D rendering on awide variety of displays. This will be described in greater detailhereinafter.

FIG. 2 illustrates the versatile 3-D video signal VS. The versatile 3-Dvideo signal VS comprises a sequence of versatile 3-D pictures . . . ,VP_(n-1), VP_(n), VP_(n1), VP_(n-2), . . . . A versatile 3-D pictureconstitutes a 3-D representation of the scene SCN illustrated in FIG. 1at a given instant. FIG. 2 illustrates details of an arbitrary versatile3-D picture VP_(n). The versatile 3-D picture VP_(n) comprises a rightpicture RP and a left picture LP, which jointly constitute a basic 3-Dthe picture. The right picture RP provides a comprehensiverepresentation of the scene SCN, which is intended for the right eye ofa human observer, whereas the left picture LP provides a comprehensiverepresentation of the scene, which is intended for the left eye of thehuman observer.

The versatile 3-D picture further comprises a depth map DM and,preferably, a background picture BG and an alpha-map, which is notrepresented in FIG. 2. The depth map DM is specifically dedicated to theleft picture LP as explained hereinbefore. The depth map DM may beregarded as a grayscale image wherein a grayscale value corresponds witha depth indication value relating to a particular pixel, or a particularcluster of pixels in the left image. A relatively low depth indicationvalue may correspond with a bright tone indicating a relatively nearbyobject, whereas a relatively high depth indication value may correspondwith a dark tone indicating a relatively distant object or vice versa.The background picture BG is also preferably specifically dedicated tothe left picture LP. In effect, the background picture BG constitutes anextension of the left picture LP in the sense that objects, which arepartially or entirely occluded, are represented in the backgroundpicture BG. The alpha-map, if present, is also specifically dedicated tothe left picture LP.

The versatile 3-D video signal VS thus comprises a sequence of basic 3-Dpictures, which correspond to the basic 3-D video mentionedhereinbefore. In addition, the versatile 3-D video signal VS comprisesan accompanying sequence of depth maps and, preferably, an accompanyingsequence of background pictures and an accompanying sequence ofalpha-maps. As explained hereinbefore, these additional elements arespecifically dedicated to left pictures comprised in the basic 3-Dvideo.

The basic 3-D video, which is comprised in the versatile 3-D videosignal VS, may be displayed on a stereoscopic display device, wherebyleft pictures and right pictures are applied to the left eye and theright eye, respectively, of a viewer. The stereoscopic display has agiven screen size and the viewer is at a given distance from thestereoscopic display device. This defines a given rendering context.

An actual rendering context may be similar to the typical renderingcontext for which the basic 3-D video is intended. In that case, asatisfactory 3-D representation of the scene SCN is obtained. Forexample, let it be assumed that the basic 3-D video is intended fordisplay in a cinema with a typical screen size of 12 meters and atypical viewing distance of 18 meters, as mentioned hereinbefore. Incase the basic 3-D video is rendered in such a cinema, a satisfactory3-D the representation of the scene is obtained.

However, in case the actual rendering context is different from thetypical rendering context for which the basic 3-D video is intended,this may result in a less satisfactory 3-D representation of the sceneSCN. This may be the case, for example, if the basic 3-D video isintended for display in a cinema as described hereinbefore, whereas thebasic 3-D video is rendered on a home video set with a screen size of 1meter and a typical viewing distance of 2½ meters. This may result in areduced depth effect, in the sense that the viewer will experience alesser degree of depth that in the cinema. Moreover, this may alsoresult in a depth shift towards the viewer, in the sense that an objectthat appears to be far behind the screen in the cinema, appears to benearly in front of the screen of the home set. Stated simply, when the3-D video that is intended for the cinema is watched at home, the 3-Dvideo will look quite different than in the cinema.

It is possible to provide some form of correction in case the renderingcontext is different from the rendering context. A new picture pair maybe generated on basis of a captured picture pair by means ofinterpolation or extrapolation. However, such a correction is relativelycomplicated, and therefore expensive, involving complex hardware orsoftware, or both. What is more, such a correction may introduceperceptible artifacts caused by interpolation errors or extrapolationerrors, whichever applies.

The versatile 3-D video signal VS, which is illustrated in FIG. 2,allows a satisfactory 3-D representation in a great variety of renderingcontexts. In terms of the aforementioned example, the 3-D video that isintended for the cinema may look similar at home. This is achievedthanks to the addition of a depth map DM, which is specificallydedicated to one picture in a captured picture pair, in this case theleft picture LP.

The depth map DM allows generating a new picture on the basis of theleft picture LP in a relatively simple and precise fashion. This newpicture represents the scene SCN from a viewpoint that is slightlydifferent from that of the left picture LP. The viewpoint may be shiftedsomewhat to the right or somewhat to the left of that of the leftpicture LP. The new picture will therefore be referred to as shiftedviewpoint picture hereinafter. In principle, the shifted viewpointpicture may represent the scene SCN from the same viewpoint as that ofthe right picture RP. In this particular case, the shifted viewpointpicture should ideally match with the right picture RP.

FIGS. 3 and 4 illustrate two different stereo modes, which are possiblewith the versatile 3-D video signal VS illustrated in FIG. 2. Thesestereo modes will be referred to as stereo mode A and stereo mode B,respectively. In each stereo mode, a pair of rendered pictures isprovided for display on a display device on the basis of a versatile 3-Dpicture. The pair of rendered pictures comprises a rendered left pictureLR and a rendered right picture RR, which are applied to the left eyeand the right eye, respectively, of a viewer. FIGS. 3 and 4 eachcomprise a horizontal axis that represents screen parallax. Screenparallax is a position shift on a display that results from a change inviewpoint. Consequently, an object in a shifted viewpoint picture asdefined hereinbefore, may be shifted with respect to the same object inthe left picture LP.

FIG. 3 illustrates stereo mode A. In this stereo mode, the right pictureRP comprised in the versatile 3-D picture constitutes the rendered rightpicture RR. That is, the rendered right picture RR is a simple copy ofthe right picture RP. A shifted viewpoint picture, which is generated onthe basis of the left picture LP and the depth map DM as mentionedhereinbefore, constitutes the rendered left picture LR.

FIG. 3 illustrates two different shifted viewpoint pictures: aleft-shifted viewpoint picture LP+S and a right-shifted viewpointpicture LP−S. The left-shifted viewpoint picture LP+S represents thescene SCN from a viewpoint that is left to that of the left picture LP.This shifted viewpoint picture has a positive parallax shift P₊₂ withrespect to the left picture LP. The right-shifted viewpoint picture LP−Srepresents the scene SCN from a viewpoint that is right to that of theleft picture LP. This shifted viewpoint picture has a negative parallaxshift P⁻² with respect to the left picture LP. FIG. 3 also illustrates aparticular case, in which the left picture LP constitutes the renderedleft picture LR, the latter being a simple copy of the first one.

In case the left-shifted viewpoint picture LP+S constitutes the renderedleft picture LR, the viewer experiences a greater depth effect than whenthe left picture LP constitutes the rendered left picture LR. There isan increase in stereo strength. Conversely, in case the right-shiftedviewpoint picture LP−S constitutes the rendered left picture LR, theviewer experiences a smaller depth effect than when the left picture LPconstitutes the rendered left picture LR. There is a decrease in stereostrength. Stated boldly, left-shifting increases the stereo strength,whereas right-shifting decreases the stereo strength.

The stereo strength may be evaluated in terms of parallax. For example,a standard stereo strength may correspond with parallax P₈ indicated inFIG. 3, which is obtained when the left picture LP constitutes therendered left picture LR. A maximum stereo strength may correspond withparallax P₁₀ indicated in FIG. 3, which is obtained when theleft-shifted viewpoint picture LP+S constitutes the rendered leftpicture LR. Parallax P₁₀ corresponds with parallax P₈ to which thepositive parallax shift P₊₂ is applied. A moderate stereo strength maycorrespond with parallax P₆ indicated in FIG. 3, which obtained when theright-shifted viewpoint picture LP−S constitutes the rendered rightpicture RR. Parallax P₆ corresponds with parallax P₈ to which thenegative parallax shift P⁻² is applied.

FIG. 4 illustrates stereo mode B. In this stereo mode, the left pictureLP comprised in the versatile 3-D picture constitutes the rendered leftpicture LR. That is, the rendered left picture LR is a simple copy ofthe left picture LP. A right-shifted viewpoint picture LP−S, which isgenerated on the basis of the left picture LP and the depth map DM asmentioned hereinbefore, constitutes the rendered right picture RR. Theright-shifted viewpoint picture LP−S has a negative parallax shift P⁻⁴with respect to the left picture LP. The stereo strength is entirelydetermined by this negative parallels shift. The right picture RP neednot play any particular role in stereo mode B. That is, the rightpicture RP may effectively be ignored in stereo mode B.

Stereo mode A is preferably used in a stereo strength range comprisedbetween the maximum stereo strength and a moderate stereo strength. Thestandard stereo strength is comprised in this range. Stereo mode B ispreferably used in a stereo strength range comprised between themoderate stereo strength and the minimum stereo strength. That is,stereo mode B can be used when a relatively small depth effect isdesired. The minimum stereo strength may correspond with the absence ofany depth effect, that is, a purely two dimensional representation. Inthis extreme case, the parallax is equal to 0: the rendered left pictureLR and the rendered right picture RR are identical.

A desired stereo strength may thus be obtained by generating a shiftedviewpoint picture and combining the shifted viewpoint picture with theright picture RP or the left picture LP depending on whether stereo modeA or B, respectively, is applied. The shifted viewpoint picture can begenerated on the basis of a left picture LP, and the depth map DMassociated therewith, according to a predefined, generic rule. Thispredefined, generic rule may be based on geometrical relationships andmay apply for all different viewpoints. In such an approach, a pixel inthe left picture LP is shifted, as it were, by an amount that isexclusively determined by the three factors: the desired stereostrength, the depth indication value, which the depth map DM providesfor the pixel as explained hereinbefore, and the predefined, genericformula. The thus shifted pixel constitutes a pixel of the shiftedviewpoint picture.

However, more favorable rendering results may be obtained in case theshifted viewpoint picture is generated in a context-dependent fashion,which takes into account one or more rendering parameters, such as, forexample, screen size. Moreover, an author, or another person, may wishto define how a given 3-D video should look in a given renderingcontext. That is, the author may express a preferred 3-D rendering,which need not necessarily correspond with a 3-D rendering based ongeometrical relationships between physical objects. 3-D rendering mayinvolve artistic preferences.

FIG. 5 illustrates a supplemented versatile 3-D video signal SVS, whichaddresses the points mentioned in the preceding paragraph. Thesupplemented versatile 3-D video signal SVS comprises rendering guidancedata GD, which accompanies a sequence of versatile 3-D pictures . . . ,VP_(n-1), VP_(n), VP_(n1), VP_(n-2), . . . . The supplemented versatile3-D video signal SVS may thus be obtained by adding rendering guidancedata GD to the versatile 3-D video signal VS illustrated in FIG. 2.

The rendering guidance data GD comprises parameters that concern thegeneration of a shifted viewpoint picture on the basis of a left pictureand the depth map specifically dedicated to this left picture. Therendering guidance data GD may specify, for example, one or moredeviations from a predefined, generic rule, which defines a defaultmethod of generating a shifted viewpoint picture. For example, differentdeviations from a default method may be specified for different stereostrengths. Similarly, different deviations may be specified fordifferent screen sizes. What is more, a deviation need not necessarilyapply to the entire 3-D video of interest. Respective deviations may bespecified for respective scenes in the 3-D video of interest, or evenfor respective 3-D pictures. The rendering guidance data GD is thereforepreferably organized into various segments, whereby a segment relates toa particular subsequence of 3-D pictures, which may constitute a sceneSCN. A segment may also relate to a particular 3-D picture.

FIG. 6 illustrates an example of a parameter set, which may form part ofthe rendering guidance data GD. The parameter set is represented in theform of a table that comprises three columns, each of which concerns aparticular stereo strength expressed as an integer value, namely 10, 6,and 5, whereby 10 represents maximum stereo strength. Each column has aheading with a shaded filling that indicates the stereo strength and thestereo method to be used for that stereo strength.

The table indicates that stereo mode A illustrated in FIG. 3 should beused for stereo strengths comprised between 10 and 6. The table furtherindicates that stereo mode B illustrated in FIG. 3 should be used forstereo strengths comprised between 5 and 0. The table further comprisesrespective lines that represent respective depth indication values. Therespective depth indication values are listed in the leftmost column ofthe table, which has a shaded filling.

The table specifies respective maximum parallax shifts Pmax forrespective depth indication values DV, for each of the threeaforementioned stereo strengths 10, 6, and 5. The respective maximumparallax shifts Pmax which may be expressed in pixel units, are listedin a white area of the column concerned. A maximum parallax shiftdefines a maximum displacement between a pixel in a shifted viewpointpicture and the corresponding pixel in the left picture from which theshifted viewpoint picture is generated. The table illustrated in FIG. 6may thus functionally be regarded as a limiting module in a shiftedviewpoint picture generator.

The maximum parallax shifts Pmax specified in the table may preventeffects susceptible to be perceived as unnatural, or effects that maycause eye fatigue, or both. As explained hereinbefore, generating ashifted viewpoint picture involves shifting pixels of the left pictureconcerned. The amount of shift typically depends on the depth indicationvalue and the stereo strength. A relatively large shift may produceunnatural effects or cause eye fatigue, or other adverse effects. Themaximum parallax shifts Pmax specified in the table illustrated in FIG.6 allows preventing such adverse effects by ensuring that the amount ofshift remains within acceptable limits.

Suitable maximum parallax shifts Pmax for stereo strengths between 10and 6 and between 5 and 0 may be obtained by means of, for example,interpolation. For that purpose, it is sufficient that the tablespecifies respective maximum parallax shifts Pmax for two differentstereo strengths in stereo mode A, such as 10 and 6 in FIG. 6, and for asingle stereo strength in stereo mode B, such as 5. There is no need tospecify maximum parallax shifts Pmax for two different stereo strengthsin stereo mode B because all maximum parallax shifts Pmax for stereostrength 0 may typically be considered as equal to 0. Stereo strength 0corresponds with mono rendering, that is, a purely two dimensionalrepresentation without any depth effects.

FIG. 7 illustrates another example of a parameter set, which may formpart of the rendering guidance data GD. The parameter set is representedin the form of a table that comprises several columns, each of whichconcerns a particular stereo strength STS expressed as an integer value,namely 10, 8, 6, 5, 3, and 1. Each column has a heading with a shadedfilling that indicates the stereo strength STS. The table furthercomprises various lines that represent various different screen sizesSZ, 30, 40, and 50 inch, which are indicated in the leftmost column ofthe table that has a shaded filling.

The table specifies respective parallax offsets Poff for the variousdifferent screen sizes, for each of the three aforementioned stereostrengths 10, 8, 6, 5, 3, and 1. The respective parallax offsets Poff,which may be expressed in pixel units, are listed in a white area of thecolumn concerned. A parallax offset defines an additional displacementfor respective pixels in a shifted viewpoint picture with respect to therespective corresponding pixels in the left picture from which theshifted viewpoint picture is generated. That is, the parallax offsetdefines an overall shift, which is to be added to a specific shift thatis obtained for a given pixel by applying a general, predefined rule forgenerating shifted viewpoint pictures. The table illustrated in FIG. 7may functionally be regarded as an output offset module in a shiftedviewpoint picture generator.

The parallax offset may compensate for a depth shift towards the viewer,which may occur when the 3-D video of interest is rendered on a screenthat has a smaller size than that of the screen for which the 3-D videoof interest was intended. For example, an object that appears to be farbehind a screen in a cinema, may appear to be nearly in front of thescreen of a home set, as mentioned hereinbefore. The parallax offsetsPoff specified in the table illustrated in FIG. 7 provide an appropriatecorrection. Suitable parallax offsets for screen sizes and stereostrengths different from those in the table illustrated in FIG. 7 may beobtained by means of, for example, interpolation.

FIG. 8 illustrates yet another example of a parameter set, which mayform part of the rendering guidance data GD. The parameter set isrepresented in the form of a table that comprises three columns, eachhaving a heading with a shaded filling that indicates a column title.The column entitled STS specifies respective stereo strengths. The othercolumn entitled Poff specifying respective parallax offsets Poff. Thetable further comprises various lines that represent various differentscreen sizes SZ, 30, 40, and 50 inch, which are indicated in theleftmost column of the table entitled.

The table specifies a preferred combination OPT of stereo strength STSand parallax offset Poff for the various different screen sizes. Thestereo strength STS is indicated by means of an integer value, like inthe tables illustrated in FIGS. 6 and 7. The parallax offset Poff may beexpressed in pixel units, or in other units. Each preferred combinationprovides a satisfactory rendering for the screen size concerned, whichmay be different from the typical screen size for which the 3-D video ofinterest is intended. An author may define the satisfactory rendering.That is, the author can express by means of the table illustrated inFIG. 8, what the 3-D video of interest should look like when rendered ona display with the screen size of interest. Preferred combination forscreen sizes different from those in the table illustrated in FIG. 8 maybe obtained by means of, for example, interpolation.

The rendering guidance data GD may further comprise an indication ofdepth map precision and depth map resolution, either explicitly orimplicitly. A depth map DM that is relatively imprecise is preferablyapplied differently than a depth map that is relatively precise whengenerating a shifted viewpoint picture. For example, there is arelatively great probability that distortions are introduced when ashifted viewpoint picture is generated on the basis of a relativelyimprecise depth map. In such a case, pixels should be shifted by arelatively small amount only, so as to ensure that any distortions arerelatively weak. Consequently, an indication of depth map precision anddepth map resolution can be used to advantage in a 3-D renderingprocess. Such an indication may also be embedded, as it were, in a tablelike the table illustrated in FIG. 7, which specifies maximum parallaxshifts Pmax.

A depth map may be relatively imprecise in case, for example, depthindication values are estimated solely on the basis of information thatis present in a two dimensional picture. A machine or a person, or acombination of both, may generate such an estimated depth map based on,for example, a priori knowledge about objects in the picture concerned,in particular with regard to their respective typical sizes. An objectthat is typically relatively large in size, but that appears asrelatively small in the picture, is probably distant. Adding depth to apicture by means of such estimative techniques may be compared withadding color to a black-and-white picture. A depth indication value mayor may not sufficiently approximate the value that would have beenobtained, a precise depth map generation technique have been used basedon, for example, distance measurements, or analysis of a stereoscopicpicture pair.

FIG. 9 illustrates a 3-D video supplementation system XSY, which cangenerate rendering guidance data GD. The 3-D video supplementationsystem XSY may further add the rendering guidance data GD to theversatile 3-D video signal VS so as to obtain the supplemented versatile3-D video signal SVS. The 3-D video supplementation system XSY comprisesa rendering guidance processor RGP, a display device DPL, and anoperator interface OIF. The 3-D video supplementation system XSY furthercomprises the storage medium STM in which a versatile 3-D video signalVS is stored, as illustrated in FIG. 1.

The rendering guidance processor RGP may comprise, for example, aninstruction-executing device and a program memory. The display deviceDPL is preferably versatile in the sense that the display device DPL mayemulate various types of display devices, which may differ in terms of,for example, screen size. Alternatively, various different types ofdisplay devices may be used in association with the 3-D videosupplementation system XSY illustrated in FIG. 5. The operator interfaceOIF may comprise, for example, a keyboard, a touch panel, a mouse or atrackball, various knobs, or any combination of those.

FIG. 10 illustrates an example of a series of steps S1-S7 that therendering guidance processor RGP may carry out for the purpose ofgenerating rendering guidance data GD. FIG. 10 may be regarded as aflowchart representation of a set of instructions, which may be loadedinto the aforementioned program memory, so as to enable the referenceguidance processor to carry out various operations described hereinafterwith reference to FIG. 10.

In step S1, the rendering guidance processor RGP prompts a systemoperator to select a particular portion of the versatile 3-D videosignal VS (SEL_VS), if needed, the system operator may select theversatile 3-D video signal VS in its entirety. The particular portionthat is selected may correspond with a particular scene, such as thescene SCN illustrated in FIG. 1. As explained hereinbefore, a 3-Drendering that can be considered as optimal for one scene, may not beoptimal for another scene. It may therefore be advantageous to evaluateand adjust a 3-D rendering on a scene-per-scene basis.

In step S2, the rendering guidance processor RGP may also prompt thesystem operator to specify data that indicates depth map precision anddepth map resolution (DM_PRC=?). Alternatively, the rendering guidanceprocessor RGP may also comprise a detection module for automaticallydetecting depth map precision and depth map resolution. As explainedhereinbefore, an indication of depth map precision and depth mapresolution can be used to advantage in a 3-D rendering process. Such anindication may also be taken into account for generating the renderingguidance data GD. For example, maximum parallax shifts Pmax, which areillustrated in FIG. 6, may be set to lower values in case depth mapprecision is relatively low, or depth map resolution is relatively low,or both.

In step S3, the rendering guidance processor RGP prompts the systemoperator to specify a rendering context (RND_CXT=?). The renderingcontext may be expressed in terms of, for example, a screen size, atypical viewer distance, as well as other rendering-related parameters.The screen size may correspond with that of the display device DPLillustrated in FIG. 10 or may correspond with another screen size, whichthe display device DPL may emulate as mentioned hereinbefore.

In step S4, the rendering guidance processor RGP prompts the systemoperator to specify a stereo strength and, optionally, a stereo mode(STS=?). The stereo strength may be in the form of an integer value in arange between 0 and 10. The integer value 0 may correspond with a purelytwo-dimensional representation, which implies the absence of any deptheffects. The integer value 10 may correspond with maximum stereostrength, which provides the highest degree of depth impression. Theinteger value 8 may correspond with, for example, a standard stereostrength that provides a default degree of depth impression, which isassociated with a faithful three-dimensional reproduction of a scene.The system operator may choose between stereo modes A and B, which weredescribed hereinbefore. The stereo mode may be predefined as a functionof the stereo strength. In that case, the rendering guidance processorRGP prompts the system operator to specify the stereo strength only.

In step S5, the rendering guidance processor RGP prompts the systemoperator to specify one or more sets of parameters (SEL_PAR) thatpotentially may form part of the rendering guidance data GD. A set ofparameters may be selected from a menu, or may be specified in a customfashion. The specified sets of parameters relate to the generation ashifted viewpoint picture on the basis of a left picture and the depthmap dedicated to this left picture, which are present in the versatile3-D video signal VS. The parameters are typically parallax related, asillustrated in FIGS. 6, 7, and 8, and may modify a depth impression. Aparticular object in the scene concerned may appear closer or furtheraway when the sets of parameters are taking into account in a renderingof the versatile 3-D video signal VS.

In step S6, the rendering guidance processor RGP causes the displaydevice DPL to display the portion of the versatile 3-D video that thesystem operator has selected in accordance with the rendering contextand the stereo strength that the system operator has defined(DPL_VS_SEL). That is, for each versatile 3-D picture in the portionconcerned, the rendering guidance processor RGP generates a renderedleft picture LR and a rendered right picture RR as illustrated in FIG. 3or 4, depending on whether the stereo mode is A or B, respectively. Indoing so, the rendering processor takes into account the sets ofparameters that the system operator has specified. This constitutes aparticular rendering of the portion concerned of the versatile 3-Dvideo. The system operator may thus evaluate if this particularrendering is satisfactory or not.

In step S7, the rendering processor determines whether the sets ofparameters in accordance with which the rendering has been carried out,should be included in the rendering guidance data GD, or not (PAR→GD?).The rendering guidance processor RGP may do so in numerous differentways. For example, in a basic approach, the rendering guidance processorRGP may prompt the system operator to indicate whether the rendering wassatisfactory, or not. In case the system operator indicates that therendering was satisfactory, the rendering processor may include the setsof parameters concerned in the rendering guidance data GD. In addition,the rendering processor may subsequently carry out step S3 and the stepssubsequent thereto, for the purpose of determining appropriate parametersets for another rendering context.

In a more sophisticated approach, the rendering guidance processor RGPmay request the system operator to specify a degree of satisfaction forthe particular rendering concerned. The degree of satisfaction may be inthe form of a score. In this approach, the rendering guidance processorRGP may carry out steps S5-S7 several times, each time for differentsets of parameters. Accordingly, respective scores are obtained forrespective different sets of parameters. In case all sets of parametersof interest have been given a score, the rendering guidance processorRGP may select a set of parameters, or the sets of parameters, whicheverapplies, that have the highest score. These selected set of parametersthey can be included in the rendering guidance data GD. The renderingprocessor may subsequently carry out step S3 and the steps subsequentthereto, for the purpose of determining appropriate parameter sets foranother rendering context.

Accordingly, the rendering guidance processor RGP may determine any ofthe sets of parameters illustrated in FIGS. 6, 7, and 8, or anycombination of those, by carrying out the series of steps S1-S7illustrated in FIG. 10. The rendering guidance processor RGP may takeover certain tasks or decisions from the system operator. That is, theremay be a higher degree of automation than in the descriptionhereinbefore with reference to FIG. 10, which is merely given by way ofexample. What is more, one or more decisions that are taken by thesystem operator may, instead, be taken by a panel representing typicalviewers. In such a case, the rendering guidance processor RGP may beprovided with, for example, a majority vote module, which determineswhether a majority of panel members find the rendering concernedsatisfactory, or not, or may be provided with an average score module,which determines an average or given by panel members.

Once the supplemented versatile 3-D video signal SVS illustrated in FIG.5 has been obtained as described hereinbefore, or otherwise, thesupplemented versatile 3-D video signal SVS may be distributed and sold,or licensed, to end users. There are numerous different ways of doingso. For example, the supplemented versatile 3-D video signal SVS may bebroadcasted by means of network, which may be wireless or wired, or acombination of those. As another example, the supplemented versatile 3-Dvideo signal SVS may be uploaded into a server from which end users maydownload the supplemented versatile 3-D video signal SVS. As yet anotherexample, a great number of storage media may be produced on which thesupplemented versatile 3-D video signal SVS is recorded. In any of theaforementioned examples, the supplemented versatile 3-D video signal SVSis preferably encoded for the purpose of data compression and errorresilience.

FIG. 11 illustrates a video rendering system RSY, which may be installedin an end user's home. The video rendering system RSY comprises adisplay device DPL of the stereoscopic type, which may require a viewerto wear a pair of glasses. A left-eye glass passes a rendered leftpicture LR, or rather a sequence thereof, to the left eye. A right-eyeglass passes a rendered right picture RR, or rather a sequence thereof,to the right eye. To that end, the display device DPL may alternatelydisplay rendered left pictures and rendered right pictures. The left-eyeglass is made transparent when a rendered left picture LR is displayed,and is opaque otherwise. Similarly, the right-eye glass is madetransparent when a rendered right picture RR is displayed, and is opaqueotherwise. As another example, the display device DPL may display therendered left pictures with a given polarization and the rendered rightpictures with an opposite polarization. The left-eye glass and theright-eye glass may then have corresponding opposite polarizations.

The video rendering system RSY further comprises various functionalentities: a storage media player PLY, a decoder DEC, a demultiplexerDMX, a shifted viewpoint picture generator SHG, a selector SEL, acontroller CTRL and a user interface UIF. All aforementioned functionalentities may form part of, for example, a home cinema device. Thedecoder DEC, the demultiplexer DMX, the shifted viewpoint picturegenerator SHG, and the selector SEL, may be implemented by means of aninstruction-executing device and a program memory. In such animplementation, a set of instructions that is loaded into the programmemory may cause the instruction-executing device to carry outoperations corresponding to one or more functional entities, which willbe described in greater detail hereinafter. The controller CTRL and theuser interface UIF may, at least partially, also be implemented in thismanner and, moreover, share the same instruction-executing device withthe aforementioned functional entities.

The video rendering system RSY basically operates as follows. It isassumed that the storage media player PLY reads a storage medium thatcomprises a coded version CV of the supplemented versatile 3-D videosignal SVS illustrated in FIG. 5. The decoder DEC receives this codedversion CV and provides, in response, the supplemented versatile 3-Dvideo signal SVS. The demultiplexer DMX effectively extracts andseparates various components comprised in this signal. The renderingguidance data GD is one such component that the controller CTRLreceives. The shifted viewpoint picture generator SHG receives variousother components comprised in a versatile 3-D picture: a left pictureLP, a depth map DM, and a background picture BG. The shifted viewpointpicture generator SHG may further receive an alpha-map, which may becomprised in the versatile 3-D picture. A right picture RP is directlyapplied to the selector SEL.

The controller CTRL determines a set of shifted viewpoint generationparameters GP and a selector control signal SC on the basis of therendering guidance data GD and rendering context data, which may beprestored in the video rendering system RSY. The rendering context datadefines a rendering context in terms of, for example, the screen size ofthe display device DPL and the typical viewing distance. The controllerCTRL may further take into account a desired stereo strength STD, ifany, for the purpose of determining the set of shifted view generationparameters. The viewer may define the desired stereo strength STD bymeans of the user interface UIF. In case the viewer does not define anydesired stereo strength STD, the controller CTRL may operate on thebasis of a default stereo strength. The set of shifted viewpointgeneration parameters GP may comprise, for example, parametersestablished on the basis of any of the tables illustrated in FIGS. 6, 7,and 8 taking into account the rendering context, which applies to thevideo rendering system RSY illustrated in FIG. 10.

The shifted viewpoint picture generator SHG generates a shiftedviewpoint picture LP+/−S on the basis of the left picture LP, the depthmap DM, and the background picture BG in accordance with the set ofshifted viewpoint generation parameters GP. The shifted viewpointpicture generator SHG may advantageously make use of an alpha-map, ifsuch a map dedicated to the left picture LP is available. The shiftedviewpoint picture generator SHG either operates in stereo mode A or instereo mode B, which are illustrated in FIGS. 3 and 4, respectively. Theshifted viewpoint generation parameters GP define a degree of shift,which may either be to the right or to the left as illustrated in FIGS.3 and 4.

The selector control signal SC expresses the stereo mode that applies.In case stereo mode A applies, the selector control signal SC causesselector SEL to select the shifted viewpoint picture LP+/−S toconstitute a rendered left picture LR. The selector SEL selects theright picture RP to constitute a rendered right picture RR in that case.Conversely, in case stereo mode B applies, the selector control signalSC causes selector SEL to select the shifted viewpoint picture LP+/−S toconstitute the rendered right picture RR. The selector SEL selects theleft picture LP to constitute the rendered left picture LR in that case.In either case, the display device DPL provides a 3-D rendering on thebasis of the rendered left picture LR and the rendered right picture RR.

FIG. 12 illustrates an alternative video rendering system ARSY or rathera portion thereof. The alternative video rendering system ARSY comprisesa display device ADPL of the auto-stereoscopic type, which does notrequire a viewer to wear a pair of glasses. Such a display devicetypically displays a set of different views MVS, whereby each view isbeamed, as it were, in a particular direction. Accordingly, the displaydevice ADPL projects different views to the left eye and the right eye,which causes a viewer to experience a depth effect.

The alternative video rendering system ARSY comprises a multiviewgenerator MVG, which receives the same components as the shiftedviewpoint picture generator SHG illustrated in FIG. 11: a left pictureLP, a depth map DM, and a background picture BG. These components may beprovided by functional entities similar to the storage media player PLY,the decoder DEC, and the demultiplexer DMX, also illustrated in FIG. 11.The multiview generator MVG may further receive an alpha-map that isspecifically dedicated to the left picture LP.

The multiview generator MVG generates the set of different views MVS,which are displayed on the display device DPL of the auto-stereoscopictype. In effect, the multiview generator MVG may be regarded ascomprising multiple shifted viewpoint picture generators, each of whichmay be similar to the shifted viewpoint picture generator SHGillustrated in FIG. 11. These respective viewpoint picture generatorsgenerate respective shifted viewpoint pictures that represent the scenefrom respective viewpoints, which are different. That is, in a diagramsimilar to FIGS. 3 and 4, each respective shifted viewpoint picture hasa particular position on the horizontal axis. It should be noted thatthe multiview generator MVG does not need to make any use of the rightpicture RP, which associated with the left picture LP. That is, rightpictures that are present in the supplemented versatile 3-D video signalSVS need not to be used for the purpose of 3-D rendering.

Hereinabove a 3D format is described which combines the advantages ofstereo and so-called image+depth formats. The embodiments belowelaborate on how such stereo+depth formats can be practicallyimplemented for use with both existing and future Blu-ray players. Theunderlying idea is to use spatial and temporal subsampling of the depthcomponent (and optionally further information such as occlusion data),hereafter also referred to as “D” and formatting it into athree-dimensional video signal comprising both stereo and depth in a2:2:1 LRD frame rate ratio.

A particular advantageous embodiment of the present invention is aimedat making use of a lower resolution representation of the video signal,in order to generate a stereo plus depth signal that fits within thebandwidth requirements of the original stereo signal. The underlyingidea is to make use of a regular 1280*720@60 Hz video stream in order toencode a 1920*1080@24 Hz stereo (LR) plus depth (D) signal.

By moreover making use of 2:1, 2:2:1 interleaving extra frame insertionswhich can contain various components (such as depth components ortransparency components)) of multiple time instances; e.g. D_(t=1) andD_(t=2), may be realized.

The LRD format as proposed earlier, generally requires more (decoding)resources then currently available in Blu-ray players. Also such Blu-rayplayers lack additional interface ports for stereo signals and depthsignals.

It is also noted that the currently used checkerboard stereo pattern hasseveral drawbacks as it does not enable use of typical auto-stereoscopicdisplays, and the 3D perception is highly screen size dependent.

Also due to the nature of the checkerboard pattern the bit-raterequirements are relatively high (at least twice the required bit-rateas that required for 1080p, 24 Hz, monoscopic video).

It is proposed to overcome both the decoding resource and interfaceproblem by using a 1280*720p time interleaved format with L′R′D′ frameswherein:

-   -   L′=spatial subsampled left image (1920*1080→1280*720),    -   R′=spatial subsampled right image (1920*1080→1280*720) and    -   D′=spatial depth.

Typically, though not mandatory, D′ comprises temporal and spatialdepth, occlusion texture, occlusion depth and transparency information.D′ is temporally subsampled with a factor 2, this meansL′+R′+D′=24+24+12 Hz=60 Hz.

Typically a Blu-ray player can decode a video signal such as a 720pimage stream encoded using MPEG. Moreover a 720p image signal is asupported video format on known interfaces, like HDMI/CEA. The proposedspatial and temporal sub sampling and interleaving of L, R and D intoone 1280*720@60 Hz L′R′D′ streams allows an implementation of thepresent invention on every existing BD player.

FIG. 13 exemplifies requirements for existing monoscopic BD playerdecoding as well as the interface (IF) throughput in Mpixels/sec. Nospecial modification needs to be made to existing players in order tosupport the above L′R′D′ encoding. It is noted that in FIG. 13 the Dframes comprise depth information (D), transparency information (T),background texture (BG) and background depth (BD). The only issueremaining is resolution of the synchronization problem.

The synchronization problem can be resolved in case the stream isencoded as depicted in FIG. 14. Here it is shown that preferably the L,R and D frames are interleaved so as to for a repeating sequence of L,R, D, L, R frames. Moreover FIG. 14 shows a preferred manner of encodingthe images. The HDMI standard has an option to indicate in the so-calledInfoframes that the image present on the interface is an originalencoded frame, and specifically I, P and B indicators are present. Inaddition signaling of the L′R′D′ encoding to the monitor or display isneeded indicating that the signal on the interface is not a regularmonoscopic 720p signal, but a 3D-720p signal according to the invention.This may need to be standardized in HDMI/CEA, however as such theinterface specification provides ample room to indicate such.

Since the above L′R′D′ signal has all the properties of a regular 720p60 Hz monoscopic signal it can be decoded by Blu-ray players and alsocan be output to the HDMI output interface thereof.

As indicated above the content of the D′ component is typically notlimited to depth but may also comprise background texture (BG),transparency (T) and additional metadata information. Metadata can beadditional image information to improve the 3D perceived quality, butalso content related information (e.g. signaling etc.).

Typical components are D ((foreground) depth), BG (background texture),BD (background depth) and T (transparency map). In principle with theproposed format these components are available at 12 Hz instead of at 24Hz. They may be temporally upsampled with known or novel upsamplingalgorithms. However, for some applications upsampling is not required.For instance, when compositing graphics (subtitles, OSD etc.) on top ofthe video it is useful to have the depth information available such thatthe graphics can be composited at the correct location, that is at thecorrect position with respect to depth.

The above can be implemented by having different (i.e. alternating)phases for depth (D) and transparency (T) as seen in FIG. 17. The figureshows a 1280×720 frame comprising depth information D1 and transparencyinformation T2. The component D1 of the 1280×720 frame is based on theD1 component from a 1920×1080 frame at time instance T= 1/24 sec. Thecomponent T2 of the 1280×720 frame is based on the T2 component from afurther 1920×1080 frame at time T= 2/24 sec.

The advantage of having D1 and T2 available from differenttime-instances is that it allows improved temporal reconstruction ofdepth by making use of transparency from adjacent time-instances, seeFIG. 17.

It is noted that not all components in the D-frame are equallyimportant. This leaves room to skip a component (always or dynamicallycontent dependent and marked with some flags), leaving room for anothercomponent to be at the full 24 Hz. This concept is illustrated in FIG.18, where transparency information from T= 1/24 and T= 2/24 are combinedwithin a single 1280×720 frame.

Thus FIG. 17 indicates the example where all components are temporallysubsampled, and FIG. 18 indicates the solution where the T(ransparency)is only spatially subsampled and not temporally (T1, T2).

New 3D BD

Also for a new to be defined 3D Blu-ray player/specification the LRDtype of format according to the present invention could become relevant.It is likely that the throughput of future BD-player systems will forreasons of compatibility and cost will be approximately 2*1080p@30 (or2*1080i@60 Hz). When the above LRD principle is applied, that isadditional information is added, an additional 11% more throughput isrequired. This is close to 2*1080p@30 Hz. Increasing the maximumthroughput with an 11% higher value could be acceptable for futuresystems, depending on the advantages.

For future 3D Blu-ray players, quality is very important. Experimentshave shown that in particular the spatial subsampling; i.e. horizontallyand vertically subsampling with a factor of 2:1 of both the depth andtransparency components may reduce quality too much (see also FIG. 21).One option to ameliorate this situation is to apply so-called quinqunxsubsampling based on diagonal filtering as illustrated in FIG. 21. Forexample 1920*1080 pixels can first, be vertically subsampled to1920*540, then diagonal filtered and quinqunx subsampled, after this weend up with 960*540 (quinqunx) samples. However these samples preservein the horizontal direction the full 1920 resolution.

Another approach would be to only subsample in the vertical directionfor depth and transparency. FIG. 19 shows how this can be implementedusing a repeating sequence of L, R, D, L, R, D, D′ frames. At the bottomthe content of the D-frames is indicated; i.e. the subsequent D, D andD′ frames. The arrows in the figure indicate the direction of predictionused in the encoding of the frames.

Within the D-frames the depth (D1, D2, D3) and transparency (T1,T2) areprovided alternating at a resolution of 1920*540 pixels. Meanwhile thebackground texture (BG) and background depth (BD) are provided at960*540 pixels.

It is noted that in this particular encoding scheme the D frames and D′frames have different contents and rates. The D′ type of frame isprovided at half the frame rate of that of L and D. The D′ frame can beused to allocate the missing time instances of depth and transparency,here D2 and T2. Please note that (some of) the components can also bequinqunx (see also appendix 1) subsampled.

Subsequently the D′ frames are interleaved with the LRD information inthe LRD stream as indicated in the GOP (Group of Pictures) codingstructure in FIG. 19 by encoding LRD-LRDD′-LRD-LRDD′ consecutively.

FIG. 19 also shows how in L R D D′ mode the depth information D and thedepth information D′ can be compressed efficiently by using D1 topredict D3 and by using both D1 and D3 to predict D2.

FIG. 15 shows some of the options for encoding video for use with 3DBlu-ray systems. As we can see from FIG. 15 the present inventionenables both the encoding of LRD (stereo+depth) for movies full HD andfor sports HD.

Finally FIG. 20 shows under option 1 an embodiment of the presentinvention wherein the D-frames for the abovementioned LRDD′ mode arebeing interleaved. FIG. 20 further shows under option 2 an embodiment ofthe present invention wherein information from 4 time instances is beingcombined, whereas the previous option only combined information from 2time instances. In this latter embodiment Y, U and V components of thevideo signal are used to carry different information, e.g. within theD²-frame the U-component carried Background Depth for T=1 whereas theV-component carries Background Depth for T=2. The individual componentsY, U and V are depicted for respective D-frames.

The contents of the respective D-frames of this second option; D¹, D²,D³, D⁴, D⁵, D⁶ are depicted below the interleaving example.

In this embodiment the background texture for four time instances (BG1₁, BG1 ₂, BG1 ₃, BG1 ₄) is packed in one frame (for 4 time instances),as a result the D frames can be used more efficiently. This embodimenteffectively capitalizes on the fact that a depth component generally isof similar size as that provided by the UV components. This even allowsone of the 2 D or T to be at full 1920*1080 res for 12 Hz, where theother time instances are at 1920*540. As can be seen in FIG. 20, thereeven may be some spare room left.

CONCLUDING REMARKS

The detailed description hereinbefore with reference to the drawings ismerely an illustration of the invention and the additional features,which are defined in the claims.

The invention can be implemented in numerous different ways. In order toillustrate this, some alternatives are briefly indicated.

The invention may be applied to advantage in numerous types of productsor methods related to 3-D visual representations. A 3-D video is merelyan example. The invention may equally be applied for 3-D still pictures,that is, 3-D photos.

There are numerous ways of providing a 3-D video picture in accordancewith the invention. FIG. 1 illustrates an implementation that comprisesa pair of cameras RCAM, LCAM. In this example, the pair of camerascaptures real pictures. In another implementation, virtual picture pairsmay be generated by means of, for example, a suitably programmedprocessor. A depth map need not necessarily be obtained by means of adepth scanner, or a similar measurement device. A depth map may beestablished on the basis of estimations, as mentioned hereinbefore inthe detailed description. What matters is that the depth map isspecifically dedicated to one picture in a pair of pictures that, assuch, constitutes a 3-D visual representation.

A depth map may either be specifically dedicated to a left picture, asin the detailed description hereinbefore, or a right picture. That is,in a different version of the versatile 3-D video signal VS illustratedin FIG. 2, the depth map DM may be specifically dedicated to the rightpicture RP. In such a variant, a shifted viewpoint picture is generatedfrom the right picture RP and the depth map DM specifically dedicated tothis picture. The background picture BG will then be also dedicated tothe right picture RP. The background picture BG may be omitted for thepurpose of, for example, data reduction or bandwidth reduction.

There are numerous different ways of providing rendering guidance data.The detailed description hereinbefore provides an example with referenceto FIG. 10. In this example, a series of steps are carried out, some ofwhich involve an interaction with a system operator. One or more ofthese interactions may effectively be replaced by an automated decision.It is also possible to generate rendering guidance data in a fullyautomated manner. It should further be noted that the series of stepsillustrated in FIG. 10 need not necessarily be carried out in the orderin which these are shown. Moreover, various steps may be combined intoone step, or a step may be omitted.

The term “picture” should be understood in a broad sense. The termincludes any entity that allows visual rendering, such as, for example,image, frame, or field.

In broad terms, there are numerous ways of implementing functionalentities by means of hardware or software, or a combination of both. Inthis respect, the drawings are very diagrammatic. Although a drawingshows different functional entities as different blocks, this by nomeans excludes implementations in which a single entity carries outseveral functions, or in which several entities carry out a singlefunction. For example, referring to FIG. 11, the decoder DEC, thedemultiplexer DMX, the shifted viewpoint picture generator SHG, theselector SEL, and the controller CTRL may be implemented by means of asuitably programmed processor or a dedicated processor in the form of anintegrated circuit that comprises all these functional entities.

There are numerous ways of storing and distributing a set ofinstructions, that is, software, which allows a programmable circuit tooperate in accordance with the invention. For example, software may bestored in a suitable medium, such as an optical disk or a memorycircuit. A medium in which software stored may be supplied as anindividual product or together with another product, which may executesoftware. Such a medium may also be part of a product that enablessoftware to be executed. Software may also be distributed viacommunication networks, which may be wired, wireless, or hybrid. Forexample, software may be distributed via the Internet. Software may bemade available for download by means of a server. Downloading may besubject to a payment.

The remarks made herein before demonstrate that the detailed descriptionwith reference to the drawings, illustrate rather than limit theinvention. There are numerous alternatives, which fall within the scopeof the appended claims. Any reference sign in a claim should not beconstrued as limiting the claim. The word “comprising” does not excludethe presence of other elements or steps than those listed in a claim.The word “a” or “an” preceding an element or step does not exclude thepresence of a plurality of such elements or steps. The mere fact thatrespective dependent claims define respective additional features, doesnot exclude a combination of additional features, which corresponds to acombination of dependent claims.

1. A method of providing a 3-D picture comprising: a picture provisionstep in which a pair of pictures (LP, RP) is provided, comprising afirst picture (LP) being intended for one eye of a viewer, and a secondpicture (RP) being intended for the other eye of the viewer; a depth mapprovision step in which a depth map (DM) specifically dedicated to thefirst picture is provided, the depth map comprising depth indicationvalues, a depth indication value relating to a particular portion of thefirst picture and indicating a distance between an object at leastpartially represented by that portion of the first picture and theviewer.
 2. A method according to claim 1, comprising: a renderingguidance data provision step in which rendering guidance data (GD) isprovided, the rendering guidance data specifying respective parametersfor respective rendering contexts, whereby the respective parametersrelate to generating a shifted viewpoint picture (LP+/−S) from the firstpicture (LP) and the depth map (DM), which is specifically dedicated tothe first picture.
 3. A method according to claim 1, the renderingguidance data provision step comprising a sub-step in which: a set ofparameters is defined for a first stereo mode (A) in which a shiftedviewpoint picture (LP+/−S), which is generated from the first picture(LP) and the depth map (DM), constitutes a rendered first picture (LR),and in which the second picture (RP) constitutes a rendered secondpicture (RR); and a set of parameters is defined for a second stereomode (B) in which the first picture (LP) constitutes a rendered firstpicture (LR) and in which a shifted viewpoint picture (LP+/−S), which isgenerated from the first picture (LP) and the depth map (DM),constitutes a rendered second picture (RR).
 4. A method according toclaim 3, the rendering guidance data provision step comprises a sub stepin which the respective sets of parameters (Pmax) are provided with adefinition of a first stereo strength range (10-6) in which the firststereo mode (A) should apply, and a second stereo strength range (5-0)in which the second stereo mode (B) should apply.
 5. A method accordingto claim 2, the rendering guidance data (GD) defining respective maximumparallax shift values (Pmax) for respective depth indication values(DV).
 6. A method according to claim 2, the rendering guidance data (GD)defining respective parallax offset values (Poff) for respective screensizes (SZ).
 7. A method according to claim 1, the rendering guidancedata (GD) comprising an indication of depth map precision.
 8. A methodaccording to claim 1, comprising: a background picture provision step inwhich a background picture (BG) is provided that is specificallydedicated to the first picture (LP).
 9. A method according to claim 8,comprising: an alpha-map provision step in which an alpha-map isprovided that is specifically dedicated to the first picture (LP), thealpha-map defining gradual transitions in a shifted viewpoint picturethat can be generated from the left picture, the depth map (DM) and thebackground picture (BG).
 10. A 3-D picture provision system comprising:a picture-providing arrangement (LCAM, RCAM) for providing a pair ofpictures (LP, RP), comprising a first picture (LP) being intended forone eye of a viewer, and a second picture (RP) being intended for theother eye of the viewer; a depth map provider (DS, RPR) for providing adepth map (DM) specifically dedicated to the first picture (LP), thedepth map comprising depth indication values, a depth indication valuerelating to a particular portion of the first picture and indicating adistance between an object at least partially represented by thatportion of the first picture and the viewer.
 11. A signal that conveys a3-D picture, comprising: a pair of pictures comprising a first picture(LP) being intended for one eye of a viewer, and a second picture (RP)being intended for the other eye of the viewer; a depth map (DM)specifically dedicated to the first picture (LP), the depth mapcomprising depth indication values, a depth indication value relating toa particular portion of the first picture and indicating a distancebetween an object at least partially represented by that portion of thefirst picture and the viewer.
 12. A storage medium comprising a signalaccording to claim
 11. 13. A method of rendering a 3-D picture on thebasis of a signal according to claim 10, the method comprising: ashifted viewpoint picture generation step in which a shifted viewpointpicture (LP+/−S) is generated from the first picture (LP) and the depthmap (DM), which is specifically dedicated to the first picture; and arendering step for rendering the 3-D picture in accordance with at leastone of two stereo modes: a first stereo mode (A) in which the shiftedviewpoint picture (LP+/−S) constitutes a rendered first picture (LR) andin which the second picture (RP) comprised in the signal constitutes arendered second picture (RR); and a second stereo mode (B) in which thefirst picture (LP) comprised in the signal constitutes the renderedfirst picture (LR) and in which the shifted viewpoint picture (LP+/−S)constitutes the rendered second picture (RR).
 14. A 3-D picturerendering system for rendering a 3-D picture on the basis of a signalaccording to claim 10, the system comprising: a shifted viewpointgenerator (SHG) for generating a shifted viewpoint picture (LP+/−S) fromthe first picture (LP) and the depth map (DM), which is specificallydedicated to the first picture (LP); and a selector (SEL) for renderingthe 3-D picture in accordance with at least one of two stereo modes: afirst stereo mode (A) in which the shifted viewpoint picture (LP+/−S)constitutes a rendered first picture (LR) and in which the secondpicture (RP) comprised in the signal constitutes a rendered secondpicture (RR); and a second stereo mode (B) in which the first picture(LP) comprised in the signal constitutes the rendered first picture (LR)and in which the shifted viewpoint picture (LP+/−S) constitutes therendered second picture (RR).
 15. A computer program product thatcomprises a set of instructions, which when loaded into a programmableprocessor, causes the programmable processor to carry out the method asclaimed in claim
 1. 16. The method of claim 1, wherein the first, thesecond picture and the depth map are provided at a resolution tuned to apredetermined bandwidth for transfer of the signal and wherein extraframes are encoded providing further data for use in rendering based onan image and depth components.
 17. The method of claim 16, wherein theextra frames comprise components of multiple time instances.
 18. A 3-Dpicture provision system according to claim 10, wherein the first, thesecond picture and the depth map are provided at a resolution tuned to apredetermined bandwidth for transfer of the signal and wherein extraframes are encoded providing further data for use in rendering based onan image and depth components.
 19. A signal that conveys a 3-D picture,comprising: a pair of pictures comprising a first picture (LP) beingintended for one eye of a viewer, and a second picture (RP) beingintended for the other eye of the viewer; a depth map (DM) specificallydedicated to the first picture (LP), the depth map comprising depthindication values, a depth indication value relating to a particularportion of the first picture and indicating a distance between an objectat least partially represented by that portion of the first picture andthe viewer, and wherein the first, the second picture and the depth mapare provided at a resolution tuned to a predetermined bandwidth fortransfer of the signal and wherein extra frames are encoded providingfurther data for use in rendering based on an image and depthcomponents.
 20. A storage medium comprising a signal according to claim19.